In liquid crystal display elements including twist nematic, super twist nematic and active matrix liquid crystal display elements, and particularly medium- and small-size portable liquid crystal display elements, the stability of the display with respect to the temperature of the usage environment is an important factor, and liquid crystal materials are being required to have lower drive voltages enabling reductions in response and power consumption, or lower drive voltages in temperature ranges of −30° C. to 0° C. or 40° C. to 80° C., reduced sharpness and smaller frequency dependency of duty cycle driving.
In particular, the liquid crystal phase temperature range (ΔT), which is the absolute value of the difference between the lower limit temperature (T→N) of the liquid crystal phase and the upper limit temperature (TN−I) of the liquid crystal phase, is important due to increased outdoor use to take advantage of the lower power consumption characteristics of liquid crystal elements. However, in the case of combining conventional materials, although it is possible to increase the liquid crystal phase temperature range, since accompanying increases in threshold voltage, increases in response speed and anisotropy of the refractive index (Δn) occur that are outside the optimum range of a nematic liquid crystal, a sufficient liquid crystal phase temperature range is unable to be obtained (pamphlet of International Publication WO 00/17287, Japanese Unexamined Patent Application, First Publication No. 2001-11450 (p. 6)). Consequently, there is a need to develop a liquid crystal composition having a wide liquid crystal phase temperature range, and a liquid crystal material optimum for outdoor use, without impairing the response speed and various other characteristics of the liquid crystal.
On the other hand, liquid crystal compounds having indane in their backbone are already known, and several of these compounds have been disclosed. However, liquid crystal compositions using these previously disclosed indane derivatives have the problems described below. For example, although a compound having a 5,6-difluoroindan-2-yl group (pamphlet of International Publication WO94/18285 (pp. 27–29), Japanese Unexamined Patent Application, First Publication No. H6-263663 (pp. 9–10)) has the characteristics of a rapid response speed despite having a comparatively large Δε, the lower limit temperature of the liquid crystal phase is quite low, thereby delaying its application as a practical nematic liquid crystal composition.
In addition, inventions have also been disclosed that comprehensively include a compound having a 4,6-difluoroindan-2,5-diyl group (European Unexamined Patent Publication No. 637585 (p. 31 to Examples), Japanese Unexamined Patent Application, First Publication No. H7-70060 (p. 30 to Examples). However, these cited references do not provide specific disclosures of the production process and physical property values of a compound having fluorine atoms at positions 4 and 6 of an indane ring. Although these cited references describe that the compound can be used as a nematic liquid crystal composition, what type of compound is combined with this compound to compose of nematic liquid crystal composition, and what characteristics are demonstrated in the case of using this liquid crystal composition are not disclosed. In addition, liquid crystal compositions using this liquid crystal composition are also already known, and examples of preferable compounds have been disclosed (pamphlet of International Publication WO 99/19420 (pp. 30–35)). However, the compound disclosed here does not have fluorine atoms at positions 4 and 6 of an indane ring, but rather has a special cyclic structure or acyclic structure consisting primarily of a substituent at position 2. Moreover, the liquid crystal composition disclosed here is a liquid crystal composition used in a ferroelectric liquid crystal element, there is no disclosure relating to a nematic liquid crystal composition.
On the basis of the above, a compound having fluorine atoms at positions 4 and 6 of an indane ring, and a nematic liquid crystal composition in which said compound is applied are not known, and there is a need to develop a nematic liquid crystal composition using a compound having a 4,6-difluoroindan-2,5-diyl group that has a wide liquid crystal phase temperature range and superior characteristics.